C++接口自动注册

#include <iostream>
#include <memory>

template <typename T> class Interface
{
  public:
    static Interface &instance()
    {
        static Interface inst;
        return inst;
    }

    static void reg(T *impl) { instance().m_impl = impl; }
    static void unreg() { instance().m_impl = nullptr; }
    static T *interface() { return instance().m_impl; }

  private:
    T *m_impl;
};

class AbscractConfig
{
  public:
    virtual void set(int value) = 0;
    virtual int get() = 0;
};

class Impl : public AbscractConfig
{
  public:
    Impl() { Interface<AbscractConfig>::reg(this); }
    ~Impl() { Interface<AbscractConfig>::unreg(); }

    void set(int value) override { m_value = value; }
    int get() override { return m_value; }

  private:
    int m_value;
};

static Impl implInst;

int main(int argc, char const *argv[])
{
    auto config = Interface<AbscractConfig>::interface();
    std::cout << "hello: " << config << std::endl;
    config->set(456);
    std::cout << "value: " << config->get() << std::endl;
    return 0;
}